Simplify the following expression: $r = \dfrac{5a}{6} + \dfrac{10a}{7}$
In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $6$ and $7$ $\lcm(6, 7) = 42$ $ r = \dfrac{7}{7} \cdot \dfrac{5a}{6} + \dfrac{6}{6} \cdot \dfrac{10a}{7} $ $r = \dfrac{35a}{42} + \dfrac{60a}{42}$ $r = \dfrac{35a +60a}{42}$ $r = \dfrac{95a}{42}$